When Mark Hacking (search) was booked into jail on suspicion of murdering his pregnant wife, he volunteered an alias that could open another chapter in his secret life.

Hacking offered the alias "Jonathan Long" when a jailer asked him, "Have you ever used another name — that could be for anything?"

Hacking didn't say why he had adopted the alias or how he used it, and jailers don't ask those questions, Salt Lake County Sgt. Rosie Rivera said on Wednesday.

City police detectives are trying to determine the significance of Hacking's alias, the latest in many deceptions they've uncovered after he reported his wife failed to turn up July 19 from an early morning jog.

Three days before she vanished, police believe Lori Hacking (search) discovered that her husband had not been enrolled in a North Carolina medical school where the couple was packing to move.

Police arrested Hacking on Monday on evidence including a bloody knife found in his bedroom, a discarded mattress and a reported psychiatric ward confession.

Hacking told a "reliable" witness there five days after his wife's disappearance that he killed Lori Hacking as she slept and dumped her body in a trash bin, a court filing revealed Tuesday.

That tip, coupled with another from a neighbor and other evidence, are leading officers to believe that they'll eventually find the remains of Lori Hacking in a county landfill.

Their methodical search through 3,000 tons of trash was to resume Wednesday night with the help of cadaver dogs that had been away — some on assignment, others on time off. The digging had started within days after Mark Hacking reported his wife missing.

It would not be unusual for a defendant to volunteer an alias during a jail booking, Rivera said, although that information more often comes from police. Hacking was booked Monday in a mental health wing of the Salt Lake County jail.

When jailers ask for an alias, "We don't ask what they've done with the name," Rivera said.

By coincidence, the jail has booked other Jonathan Longs in the past, but none are believed to have been Mark Hacking, she said.

"We book 30,000 people a year, so the odds of people having the same name are pretty good," she said.

The other Jonathan Longs used various middle initials and had different dates of birth than Hacking's, who was born April 24, 1976, the fifth of seven children to a respected Mormon family in Orem, Utah. His father, Douglas Hacking, is a pediatrician.

Jailers determined there was no criminal record under the name Jonathan Long and Hacking's date of birth, Rivera said.

They took Hacking's fingerprints at booking, and those fingerprints were fed into a Utah and national criminal database. If the system matched Hacking's fingerprints to another crime, solved or unsolved, it would alert Utah authorities, but hasn't done so, she said.

One thing is certain: Hacking does not have a criminal history in Salt Lake County (search), she said.

The investigation was to shift to a municipal landfill Wednesday night.

Another tip leading authorities there came from a neighbor who said someone might have used his trash bin to dispose of a body. The neighbor based that conclusion on a foul-smelling liquid in the bottom of the bin after the trash was collected the day the woman was reported missing.

The witness who allegedly heard Hacking's confession told investigators he confided to him July 24 during a community-wide search for his wife that drew thousands of volunteers.

This account, provided in a police affidavit used to arrest and jail Hacking until he can be charged, also states that investigators found human blood on a knife in the bedroom of the Hackings' apartment and on the couple's headboard and bed rail.

Blood found in the bedroom matched traces of blood found in Lori Hacking's car, according to the probable-cause statement.

The affidavit said police found a mattress in a trash bin near the Hackings' apartment that matched the serial numbers of the box spring recovered from inside the apartment.

Police have said Hacking was buying a mattress less than 20 minutes after he first called them to report his wife missing. He had told her co-workers that he found her car in a park and was there looking for her.

Days later, it was discovered that Hacking had lied about graduating from the University of Utah and lied about being accepted at a medical school in North Carolina, where the couple was to have moved within days.

A judge set Hacking's bail Tuesday at $500,000, Salt Lake County District Attorney David Yocom said.

Hacking's attorney, D. Gilbert Athay (search), did not return a phone message.

Yocom said he still is reviewing the case and asked police to conduct more witness interviews.

The prosecutor said he was uncertain he could file charges in the 72 hours required by law after Hacking's arrest and may ask the court for an extension.

Yocom declined to say whether he would seek the death penalty, but did say the wishes of the victim's family are given great weight in such decisions.

There also is a question whether the circumstances of the case would support a capital homicide charge. Yocom would not address the strengths of the case.

However, Lori Hacking had told friends she was five weeks' pregnant, based on a home pregnancy test.

If her body is found and the pregnancy is confirmed, prosecutors could add an additional murder charge, which might provide one of the possible aggravated circumstances required for capital homicide.