Eva Reyes, 71, also said the legal system that allowed her son, David Maust, to leave prison after two previous murder convictions bears some responsibility for his latest alleged crimes.
Maust is accused of luring teenagers into his Hammond, Ind., home by offering them alcohol and drugs. Last week police unearthed the bodies of three missing teenagers from beneath a concrete slab in his basement.
Maust, previously convicted of murder in 1974 and 1981, had been free since 1999. Reyes said she fears her son may have killed more people.
"If he's been out since '99 like they say, there's more someplace," Reyes told The Associated Press.
Reyes said she has not talked with her son since the mid-1980s, when she visited him in prison in Illinois.
The remains of the bodies found in Maust's basement were identified as those of Michael Dennis, 13; James Raganyi, 16; and Nick James, 19.
Maust, 49, is charged with murder in Raganyi's death and is being held without bond. No other charges have been filed.
Reyes said that if found guilty, Maust should be put to death. "I love David, but yes, that would be the right thing to do for him," she said.
Maust was convicted in Illinois in the 1981 slaying of a teenage boy and was held in mental institutions two years before he was judged fit to stand trial.
In 1974, he also was convicted of killing a boy in Germany while stationed in the Army. He served more than three years at the federal prison in Fort Leavenworth, Kan.
"When he was in prison (in Illinois) they said he would never get out," Reyes said. "He conned a judge ... They should charge the judge for the murders, too."