BOISE (AP) - A judge has entered a not guilty plea for a 22-year-old Idaho man charged with killing a former Arizona power company executive, his wife and their adult son at their Boise home.

Adam Dees of Nampa, who appeared in 4th District Court on Thursday, declined to enter a plea, so 4th District Court Judge Sam Hoagland entered the plea on his behalf.

Dees is charged with three counts of first-degree murder as well as robbery and other crimes.

Prosecutors allege Dees killed Theodore M. Welp, 80, Delores Elaine Welp, 77, and Thomas P. Welp, 52, on March 8 or 9. The bodies were found March 10.

Dees has been jailed since March 11 when he was arrested and charged with grand theft and other crimes. Authorities said he was found with credit cards linked to the Welp family, and that Dees tried to sell Elaine Welp's engagement ring, which was recovered at a local jeweler.

All three victims were shot in the head and beaten with a baseball bat, and Thomas Welp was also stabbed in the neck, according to an April 8 grand jury indictment charging Dees with the three counts of first-degree murder.

Hoagland set Sept. 29 as the start for a trial that Deputy Ada County Prosecutor Jean Fisher said would take two months.