Was Amy Robsart's death suicide, accident or murder?

Amy Robsart was the wife of Robert Dudley. They married in 1550. She lived at Cumnor Place, Berkshire, while her husband attended court as Queen Elizabeth's master of the horse and the Queen's favorite. On Sept. 8th, Amy Robsart was found lying dead at the foot of the staircase with her neck broken. At the time of Amy's death, Queen Elizabeth was pregnant with Francis Bacon, Dudley's child. Elizabeth and Dudley were married previously while incarcerated in the Tower during Queen Mary's reign, but Dudley was married. In order to legitimize the child, the couple would need to marry when Dudley was not tied. Interestingly, the couple marry for a second time about two weeks after Amy Robsart's death. "Francis was born in the January following, Dudley marrying the Queen privately at the House of Lord Pembroke at the end of September." (Dodd, Alfred, The Marriage of Elizabeth Tudor, Rider & Co., London, 1940.)
Alfred Dodd writes in his book, The Marriage of Elizabeth Tudor, "It was generally believed at the time that she was murdered, and that Dudley, if not Elizabeth herself, was an accessory to the crime. This belief receives some support from certain discoveries made in the archives at Simancas, which indicate that a plot to poison her was actually entered into before her death. (Chambers's Encyclopaedia, Vol. VI, p. 566.)"
Robert Dudley rarely visited his wife and because of his neglect she spiraled into despair and depression. She most likely was aware of Dudley's ambitions and the Queen's high regard for him. In addition, she was said to have been ill with possibly breast cancer. All of these combine to form an unhappy, lonely person. It was a Sunday and she sent all the servants into town for a festival that was happening that day. When they returned, they found her at the bottom of the staircase. Did she throw herself down the stairs in hopes of throwing her life away? Did she just chance to slip and fall? Did Elizabeth's Secretary, William Cecil, Dudley's enemy, start rumors of murder and intentionally loosen the railing spindles in hopes that Amy would lean on them and fall?
Francis Bacon wrote some lines in cypher pertaining to the death of Amy Robsart. The following is an excerpt from Orville Owen's Sir Francis Bacon's Cipher Stories, Vol. II:
"Some did cry, 'Ayme! Ayme!'
'This, by his voice, should be my lord,' said she, And from the great chamber to the landing ran; And thinking the pillars steadfast and firmly stay'd, Did lean upon the rail and there awhile As on a pillory looking through she stood; But it, not capable to sustain a rush Or the impressure of her palm, went down. On the slippery standing She tremblingly a moment stood and cried to heaven; Then from human help exiled, with earnest moan She on the sudden headlong dropt Down, down, down to the hard court beneath, And her neck asunder broke And all the bowels in her body brast."

Robert Cecil Murdered Queen Elizabeth Tudor

I came across a very interesting account of an incredible story of murder in a cypher written by Francis Bacon. The cypher story tells of how Robert Cecil drugged Queen Elizabeth and then strangled her to death. The cypher story can be found in the book, Sir Francis Bacon's Cipher Stories, Part 2, by Orville W. Owen, pp174-189, Howard Publishing Co., New York, 1894.
The above picture shows Robert Cecil, 1st Earl of Salisbury, (1 June 1563 -- 24 May 1612). who was the son of William Cecil, 1st Baron Burghley. Robert Cecil served Queen Elizabeth as her Secretary of State and he later served James I.
The excerpt I found is as follows: 

". . . At the end her death was miserable, Terrible and revolting to human nature, In that her melancholy desire of life And impatience of sickness Wore the appearance of lunacy."
"Stay a little, your lordship. I think you mentioned that Cecil Rid her of life. Hasten on to the account. Come, come sir! It is unseasonable and puerile hurry To snatch at the first apple that comes within reach; For though it be true that this beast, By the sufferance of the highest King of kings, By the skillful use of poison did disable her, And then by violent means bereft her of life.. . . "
Francis Bacon is having a discourse with the physician who attended Queen Elizabeth. He recounts their conversation in the cypher as follows:
"Didst thou, doctor, hear this singular speech?"
"O, yes, I heard all, and more too. I heard Master Cecil say, 'Let her not live.' Then they come unto me and commanded me to begone. So I yield, being sore dismayed, And go lamenting out. And I fear me That they killed her after I was expelled."
"But, loyall sir, Was not someone else there? Didst thou leave these varlots alone with her?"
"There was a lady, sir, near her."
"Indeed! What may be her name?"
"I did hear her called Grace."
"I sought out this maid And call at her house, which doth stand By Christ Church, and said to her, 'I hear you did chance to see The death of the queen?'"
"Why, sir, why, man, I understand you not. Speak softly. I will be lost, quite lost, If that devil knew mine eyes Did see him slaying her. Who told you , sir?"
"Be patient; I am loathe to tell you Whence it come, But I must know the truth; therefore Dally not with me, But give me the cruel story."
"Sir, give me leave, I beseech you, To show it by some mighty precedent. Some three ages since the king Had a servant that served him Long and faithfully. Well, one night 'T is said, sir, this good man's life Was taken by his foe."
"But how? Say how. Show not how quaint an orator you are, But answer; who was the man?"
"Sir, you that are so shrewd, cannot you guess Humphrey, Duke of Gloucester's name?"
"Upon my soul, They did kill him in bed."
"Thus didst he, our sovereign, With his hands about the circle of her neck, The villain did stifle her, Sealing the sweet breath that was embounded In her beautious clay."
"Did he with his hands Choke his dear lady sovereign?"
"These two eyes beheld this evil murder."
"I pray thee, what did the creature do first?"
"After the physician had hurried out He locked the doors."
"List to me; If the doors were locked and you Shut out, how did you see?"
"I was not shut out. I did not go when they bid us to, But hid myself under the desk That's covered with Turkish tapestry, Which stands in her chamber, Where I saw The whole vile murder committed. O, dear heaven! I saw him cast her on her back, And in spite of her bootless fight, He with his cruel hands Her fair throat did strongly bind. The shamefast band may not be shaken off, Though she strongly struggled Both with foot and hand, And with all the might she had She strove him to withstand and save her life. The vile villain Reviled her, and bathed in blood and sweat The sunshine of her clear countenance First did win away in luckless death. Still did he hold her Till she was still in death. Then when he discovered that his force Her life had reaved, He, like a dead man, frozen stood. Then in a twinkling, all in deadly fear, He ran unto the closed door, The key did turn, rudely thrust it open And did fly from forth the chamber. Behind his back I crouch as he passed by, And with trembling heart Softly slide after him. I fear his roving eye may on me glance, And sir, I thought How easily the villain might Thrust on me the bloody crime. The very thought turned my blood cold. Ah! Woe is me! I might have tried to call for help And save her life."
"A plague on you! Why did you not?"