JOLIET, Ill. — Jurors said Friday that comments Stacy Peterson made before her 2007 disappearance played the decisive role in convincing them to convict her husband, former police officer Drew Peterson, of killing his former wife.

Peterson was convicted of first-degree murder on Thursday after a six-week trial that was the first of its kind in Illinois history. Prosecutors based their case on normally barred hearsay, which was only allowed after the Legislature passed a law specifically tailored to Peterson’s case.

The strategy was risky and grew in large part from a lack of physical evidence collected in the case after investigators initially deemed Kathleen Savio’s death an accident. Prosecutors claimed the hearsay would allow Savio and Stacy Peterson — who is presumed dead — ‘‘to speak from their graves’’ through family and friends.

Jury foreman Eduardo Saldana, 22, said the women’s comments were ‘‘extremely critical’’ in deliberations and in his decision to convict Peterson. He said he was one of four jurors who initially had reservations given a lack of physical evidence tying the former police officer to Savio’s death. But Saldana said the more he thought about hearsay testimony from Stacy Peterson’s pastor, the more compelling he found it.

The Rev. Neil Schori testified that Stacy Peterson told him weeks before she went missing that her husband got up from bed and left the house about the time of Savio’s death and then returned to stuff women’s clothing in their washing machine. Peterson also coached his wife for hours on how to lie to police, Schori told jurors.

Defense lawyers have said the presentation of hearsay, or information reported by a witness that is not based on the witness’ direct knowledge, undercut Peterson’s constitutional rights because he couldn’t directly confront his accusers — namely, his third and fourth wives. Attorneys for Peterson have vowed to appeal.