An embattled former bank executive committed suicide by crashing his van after killing his wife and making failed attempts to asphyxiate their four children in a garage, then slaying them individually, authorities said Tuesday.

Steven Sueppel, who had been charged with embezzlement, was missing after his family's bodies were discovered Monday morning. His van was found wrecked and ablaze on Interstate 80 about nine miles away, and police said they used dental records to identify the burned body inside as Sueppel's.

In a news conference Tuesday, investigators said they believe he killed his wife, then tried to kill himself and his children by asphyxiating them with carbon monoxide in the garage. When that failed, he killed the children one by one in the house.

Investigators think the children died by "blunt force trauma," though autopsies are not complete, Lt. Jim Steffen said. Two baseball bats might have been used and were being examined, he said.

"Steven is probably the only one who knew why he did what he did, and I don't know that we're ever going to be able to determine the real reason why this happened," Steffen said.

After the children died, Sueppel tried to drown himself in the Iowa River without success. He then made a 911 call directing officers to his home and a few minutes later crashed into a freeway abutment.

Sueppel left a long note in the family's kitchen addressed to no one in particular. He also left voice mail messages at the family's home, at the bank where he once worked and at the law office of his father and brother.

One of the messages indicated Sueppel believed his family was in heaven, Steffen said.

"He did indicate in his note that ever since his problems came to light that he was having trouble dealing with this issue, but again no specific incident or cause was identified as to why it happened now," Steffen said. "He apologized ... numerous times."

Police identified the children as Ethan, 10; Seth, 8; Mira, 5; and Eleanor, 3.

Their bodies were found throughout the home. Two were in upstairs bedrooms, one in a basement bedroom and another in a basement toy room. Sheryl Sueppel's body was found in the master bedroom.

Steffen said a family friend was the last to see Steven Sueppel and at least one of the children at 8 p.m. Sunday at the Sueppel home. The friend didn't sense any questionable behavior.

The 911 call made early Monday alerting police to the family's home at the edge of Iowa City was made from Steven Sueppel's cell phone, police said.

A recording of the call was released Tuesday:

"This is 911. What's the location of your emergency?" the female dispatcher said.

"Hello, am I talking to Iowa City?" the caller responded.

The dispatcher again asks the location.

"Iowa City, Iowa," the man said.

The dispatcher asked for an address.

"629 Barrington Road," the man said. "Please go there immediately."

The dispatcher asked what's going on there and the caller hung up.

About six minutes after the call, more 911 calls poured in to dispatchers, reporting that a minivan had crashed into a concrete abutment in the median of Interstate 80 east of town.

One caller sobbed as she described seeing the burning minivan, which had crashed head-on into the abutment.

"Oh, my God, the car's on fire," the woman sobs. "I was going to stop and help but the car's on fire."

Court records show that Steven Sueppel, 42, was indicted last month on charges of stealing about $560,000 from Hills Bank and Trust in Johnson County, where he was vice president and controller.

He pleaded not guilty to embezzlement and money laundering in U.S. District Court and was released on a $250,000 personal bond. The government was also seeking the forfeiture of the money he was accused of stealing.

His trial was scheduled for April 21.

A funeral for all six family members will be held at 10 a.m. Saturday at St. Mary's Catholic Church in Iowa City, according to Lensing Funeral & Cremation Service. Burial will be at St. Joseph's Cemetery.