After successfully getting a serial rapist's bail increased Thursday morning, the next challenge facing prosecutors will be proving what 60-year-old Thomas Warren was attempting to do when he was caught in a woman's Chester Creek-area yard a week ago.  

Police arrested Warren on July 19 after watchful neighbors observed him acting suspiciously, putting on gloves and entering a woman's property, leading them to call 911. 

Officers found Warren was carrying a three-foot length of coiled rope.

To prosecutors, the seemingly insignificant detail of his latest case is a chilling correlation to his more than three decades old criminal past.  

According to court documents, Warren raped multiple women during the 1980s. He was known to break into their homes and wait for them to return. In one assault, he used cord or twine to restrain the victim.  

RELATED: Serial rapist arrested with rope in Anchorage woman's backyard 

After scoring a two out of 10 on the state's risk assessment tool, which is considered low-risk, Warren's bail had been set at an unsecured amount of $1,000. Unsecured bonds allow defendants to be released without paying any money up front. 

Prior to a recent legislative fix that gave pretrial bail discretion back to judges, Warren would have qualified for mandatory release, based on his current charges of trespassing and attempted burglary. 

Thursday morning, Anchorage Assistant District Attorney Michael Ebell urged District Court Judge Michael Logue to use his discretion to increase Warren's monetary bail. 

"His priors from 1988 when he pled no contest share a chilling similarity to the conduct in this case," said Ebell. 

Public defender Shana Bachman argued electronic monitoring through the Pretrial Enforcement Division (PED) would suffice. 

"They're drawing parallels to something that happened in 1988-- something that is a lifetime removed now from Mr. Warren," said Bachman. 

Judge Logue set bail at a total of $10,000 that must be paid in full in order for Warren to be released. If he posts bail, Warren will be ordered to house arrest with GPS electronic monitoring through PED. Now, Ebell says the state is looking into charging Warren with attempted sexual assault. 

"The jury's going to have to find beyond a reasonable doubt that he intended to commit burglary under his current charges, or that he intended to commit sexual assault if those charges are eventually brought," explained Ebell, "That can be really difficult to prove, but we can use circumstantial evidence, and there are unique circumstances, and this is one where we are allowed-- in attempted sexual assault cases-- to admit to a jury prior criminal conduct." 

He said Warren challenges the modern picture of rape they typically instruct jury members on. A majority of the sexual assault cases tried in Anchorage involve a defendant and accuser who know each other, rather than a stranger hiding in the shadows to attack. 

"This is extreme. This is as dangerous as it gets as far as public safety is concerned," said Ebell. 

An Anchorage Daily News article dated August 22, 1987, reports Warren's plea of 'no contest' to three rape charges.

An Anchorage Daily News article from 1987 reports Warren had been dubbed the "Clipboard Rapist" after accidentally leaving his notes behind at a victim's house-- a mistake that ultimately led to his identification as a suspect in several rapes. 

"When the victim called 911, the police dispatcher asked her if she had closed and locked her door. The woman did so, according to police reports, just moments before Warren returned for the clipboard. He stood pounding at his victim's door as police raced to the scene. He was later arrested at his job," said the article written by Sheila Toomey. 

Warren pleaded "no contest" in the rapes of three women for a sentence of 40 years. In exchange, prosecutors agreed to not charge him in connection with nine other sexual assaults. 

Warren was released on mandatory parole in 2013 but has been in and out of custody due to violations of his conditions, spending only about 18 months out of custody since then. 

While it's been a little over three decades since Warren was charged, Ebell says an assistant district attorney before him prepared for the day Warren would be released. 

According to the plea agreement Warren signed, he was required to provide Anchorage Police with taped confessions for the sexual assaults he wasn't being charged in. 

The prosecutor, Steve Branchflower, told The Anchorage Daily News "the confessions will be made part of the record so a future parole board will realize they are dealing with a serial rapist". 

Convicted serial rapist Thomas Warren, 60, hides his face behind papers during his bail hearing on July 26, 2018. (Photo credit: KTVA Photojournalist Jared Mazurek)

"As long as some of that evidence still exists, he took extra steps to ensure that we had more information than we would have had as a result of the plea agreement, rather than less," said Ebell. 

Ebell said the Anchorage District Attorney's Office, Alaska State Troopers and Anchorage Police are all searching for any records they have on Warren from the '80s. 

In his bail memorandum, Ebell wrote, "Investigation is ongoing, but it seems increasingly likely that evidence of an attempted assault will be presented to the grand jury for consideration". 

The maximum punishment Warren faces for his current charges is a sentence of five years. If charged with attempted sexual assault, he faces a maximum sentence of 99 years. 

KTVA has submitted an open records request to the Anchorage Police Department seeking to gain access to Warren clipboard notes and the taped confessions-- if they're found. 

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