A police source has told ABC News that they have recovered the murder weapon. Though more than one gun was recovered, they believe he used only one in the attack, a semi-automatic handgun.
Authorities said the attack was a planned ambush.
"We don't believe he was targeting them in particular," Troyer said. "We just believe he was out to kill some police officers execution style."
Police learned after the attack, Troyer added, that Clemmons had bragged to others the night before the shooting that they should watch the news "because he was going to go kill some cops."
Troyer said people who heard Clemmons' alleged warning called in the tip to police after the shooting.
"They are people they were hanging out with the night before," he said. "They didn't believe him and thought he was crazy."
Troyer said police have interviewed the people who heard the threat, but would not release their names or comment on their identities other than to say they were acquaintances of Clemmons.
Troyer said police narrowed in on Clemmons as a suspect Sunday, their suspicions solidified by news that Clemmons was suffering from a gunshot wound.
The Lakewood Police Department is a small force and the deaths represent a loss of 10 percent to 15 percent of the department. The four officers killed were parents to a total of nine children. Their deaths, Troyer said, should never have happened.
In a news release, the sheriff's office said Clemmons has an extensive violent criminal history from Arkansas, including aggravated robbery and theft. Clemmons also recently was arrested and charged in Pierce County in Washington state for third-degree assault on a police officer and second-degree rape of a child.
Clemmons had been released from custody six days ago, bonding out despite an outstanding warrant from Arkansas, where he was pardoned by then Gov. Mike Huckabee nine years ago after serving 11 years of a potential 60-year sentence.
Troyer faulted the state of Arkansas for not acting on the outstanding fugitive warrant for Clemmons after Washington police notified them that he was in custody.
"We know here in Washington we didn't do anything wrong," Troyer said. "We've arrested him multiple times."
In a statement released overnight, Huckabee called the murder of a police officer "the worst of all murders in that it is an assault on every citizen and the laws we live within."
"Should he be found to be responsible for this horrible tragedy, it will be the result of a series of failures in the criminal justice system in both Arkansas and Washington State," Huckabee said, saying that Clemmons met the conditions for commutation and parole at the time. "It appears that he has continued to have a string of criminal and psychotic behavior but was not kept incarcerated by either state."
Marion Humphrey, the Little Rock judge who urged clemency for Clemmons in 2000 told ABC News today that he was horrified and hurt that the man he recommended for leniency would be accused of such a crime.
"I did what I did, and I stand behind what I did. I regret what has happened and I acknowledge responsibility for what I did," Humphrey said. "At the time he appeared to me to be a person who was trying to get his life back together."
Humphrey, also a Presbyterian minister who presided over Clemmons' wedding, said his consideration was based on his belief in mercy and Clemmons' age at the time.