BALSAM LAKE, Wis. (AP) — Police on Thursday expressed regret that investigators taking part in an exhaustive all-day search amid blistering heat did not force open the trunk of a car where a missing western Wisconsin toddler was later found dead.

Two-year-old Isaiah Theis disappeared Tuesday night. A Polk County sheriff's deputy found his body about 10:15 p.m. Wednesday in the trunk of a locked car parked outside the boy's home — where his father repairs cars — when the owner came to retrieve it.

Searchers had looked into the car and checked the area around it several times, Sheriff Peter Johnson said in a statement.

But they did not look in the trunk. Chief Deputy Steve Moe told reporters at a news conference that, in hindsight, he wished they had. But he said searchers were operating under the assumptions that Isaiah had wandered off Tuesday evening, which he had a tendency to do, and that all the cars were locked.

He said deputies did not have access to the keys, but he wasn't certain whether the keys were on the property.

"Would we liked to have forced entry to the car? Yeah, from my personal perspective," Moe said.

Moe declined to speculate how Isaiah ended up in the trunk and wouldn't say whether investigators consider his death an accident or the result of foul play.

"I know that there's strong interest in what caused it and what things led to the boy getting in that car," he said. "It's just too early."

The chief deputy said the autopsy was being expedited but he didn't expect results Thursday.

"A full autopsy has been requested and it would be inappropriate for anyone to speculate as to the cause and nature of death until that examination has been done," the sheriff's own statement said.

Isaiah's maternal grandfather, Paul Krey, told KARE-TV (http://kare11.tv/18ni2Ql ) that the car belonged to a customer of his son-in-law, who is a mechanic and works out of a shop on his property. Krey said the car was parked there and waiting to be fixed. All the Theis children were comfortable hanging around the shop and spent plenty of time around the vehicles while their father worked, the grandfather said.

The boy's mother told investigators Isaiah was last seen about 7:30 p.m. Tuesday while playing with his 7-year-old brother at their home near Centuria, which is about 60 miles northeast of St. Paul, Minn.

About 2,450 civilian volunteers helped search the fields and woods surrounding the family's home throughout the day Wednesday, the sheriff said.

Debbra White, 51, of Milltown, Wis., left a teddy bear and a wind chime at a makeshift memorial near the scene. White told the Star Tribune of Minneapolis that she lost her 8-year-old son more than 20 years ago when he drowned in the St. Croix River.

"There's nothing I can say to bring their son back," White said.