A man accused of killing seven women over a 21-year period confessed to a former cellmate that he had committed murder and that it turned him on to beat and choke women, prosecutors said.

Walter E. Ellis told former cellmate Frederick Bonds in 1998 that he had killed women, and Bonds said Ellis was upset when he learned prison officials planned to take DNA samples from inmates, prosecutors said in court documents filed Feb. 5.

Ellis and Bonds shared a cell for several months when Ellis was serving time for allegedly hitting his girlfriend in the head with a hammer.

Ellis' attorney, Russell Jones, filed a motion seeking to bar Bonds' testimony, saying it wasn't relevant to the case.

A judge is expected to hear arguments on the matter at a Friday hearing.

Ellis, 49, has pleaded not guilty to first-degree intentional homicide or first-degree murder in the deaths of the women, who were killed between 1986 and 2007. Investigators suspect they were prostitutes, but some of the victim's family members dispute that. If convicted of either charge, he would face a mandatory life prison sentence, although the judge could decide whether to allow the possibility of parole.

Prosecutors say Ellis' semen was found on six of the seven women he's charged with killing. His blood was found on a can of pepper spray found at the scene of the seventh slaying. Investigators believe all the victims were strangled, and that one was also stabbed in the neck.

Ellis was in prison between 1998 and 2001, and Corrections Department officials should have collected a DNA sample at that time. Agency records showed a sample was taken from Ellis on Feb. 4, 2001, but the Justice Department discovered it had nothing from him and launched a more comprehensive probe of the entire database.

Ellis wasn't arrested until Sept. 5, 2009 after the Milwaukee police department's cold case unit sifted through thousands of cases and tested the DNA of more than 100 people.

Prosecutor Mark Williams said he didn't know why Bonds was in prison. The Department of Corrections couldn't immediately say why he was in prison.

Jones said the credibility and motives of someone relating alleged jailhouse conversations has to be questioned.

"All of sudden Walter is a target and anyone is going to try to put their name on this," he said.

Jones also filed a motion seeking a change of venue for the trial, claiming the pretrial publicity has tainted the jury pool. He also has indicated he wants to include testimony to point to the possibility of other suspects and require medical examiners and other expects to have to be cross examined about reports or tests done — some decades ago — in order for them to be admitted.

Jones is seeking to exclude testimony from 10 potential state witnesses, including two who would say Ellis was paranoid of the police. Joseph Hardmon, the son of one of Ellis' ex-girlfriends, told authorities that Ellis would hide in the basement when he saw police and he even hollowed out the inside of a couch to make a hiding space.

Jones said it was reasonable for Ellis to be afraid of the police since he was involved with prostitutes and drugs, but that his fear doesn't mean he killed the women.

Another state witness is Napoleon Clark who would testify that Ellis asked him — and he agreed — to pretend he was Ellis and give a DNA sample in his name in 2000 or 2001.

The witnesses are unable to connect Ellis to the women the days they were murdered so therefore are irrelevant, Jones said.