A Connecticut inmate accused of being a serial killer allegedly confessed to his fellow inmates that he killed seven people in 2003, including one whose body he kept for two weeks in a van he allegedly called his “murder mobile,” according to an arrest warrant obtained by PEOPLE.

William Howell, 45, a drifter and Virginia native known to other prisoners as “Hillbilly,” allegedly described himself to a cellmate as a “sick ripper,” according to the warrant, which was released on Friday. Howell also allegedly told a cellmate that “there was a monster inside of him that just came out,” the warrant states.

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Howell allegedly told the inmate that if he hadn’t been caught, he would have gone across the country to kill others, the warrant adds.

Howell was charged with multiple felony murder counts after authorities discovered the remains of seven people hidden behind a New Britain shopping center, police said in a statement on Facebook.

Howell s attorney did not return calls seeking comment from PEOPLE on Monday, and a spokesperson for state s attorney s office tells PEOPLE that the office does not comment on pending criminal cases.

Howell is currently serving a prison sentence for killing Nilsa Arizmendi, whose body was among those found behind the shopping center – a site police say Howell called his “garden.” Authorities said that three bodies were found in 2007 and the other four were discovered this past April.

On Friday, Howell was arraigned in New Britain Superior Court on the murder charges in connection with the deaths of the other six victims; all of them disappeared in 2003 when Howell was working odd jobs in central Connecticut.

The warrant paints a grisly picture of the victims’ deaths: It alleges that Howell used sticks to sexually assault three of the women he killed. Police said all of the victims put up a fight against him in the van, where most of the alleged slayings took place.

Howell allegedly told an inmate that his first victim was a woman who he raped in the van before strangling her and hitting her in the head with a hammer, according to the warrant. He allegedly said he slept next to the woman’s body in the van and called her his “baby” before cutting off her fingertips, breaking her bottom jaw and disposing of her remains.

The arrest warrant further claims Howell bragged in prison about strangling a man he initially believed was a woman; Howell allegedly killed the man after his wig fell off during a sexual encounter. He allegedly told an inmate he also killed a prostitute after raping her with a shock absorber.

In 2005, Howell pleaded guilty to manslaughter in the death of Arizmendi: His arrest warrant for that crime states that he beat her with a hammer in the van, records show.

Howell didn’t speak or enter a plea at his Friday arraignment. His bail is set at $10 million.

The family of Joyvaline Martinez, one of the victims, attended the arraignment. Martinez’s sister Sandra told WFSB-TV that she and her family “faced a monster,” referring to Howell.

Sandra said she has looked forward to the day she would see her sister’s killer, but she has also dreaded it.

“Why did you do this to my little sister? She didn’t deserve it, no one deserves to go through the torture that he put her through,” said Sandra, who added, “I hope he never gets out of jail and he rots.”

In addition to Martinez and Arizmendi, the other victims include: Diane Cusack, 53; Melanie Camilini, 29; Mary Jane Menard, 40; Danny Whistnant, 44 and Marilyn Gonzalez, 26.