Former FBI profiler Clint Van Zandt says there is a distinct possibility Jessica's killer either watched or even attended the service.
Van Zandt noted a large community event such as the memorial may actually attract Jessica's killer.
"Whoever is responsible for that young girl's death could even show up at that ceremony," Van Zandt said. "So law enforcement is going to be there."
Law enforcement was visible inside and outside the memorial.
The FBI believes the killer is closely following all the media coverage, and may want to see the spectacle for himself.
Westminster police and the FBI are urging the public to keep their eyes open.
Former FBI Colorado Special Agent in Charge Bob Pence says now is the time to keep your kids close because whoever killed Jessica is still out there.
"I think everybody needs to be careful. In this case we have what I consider a pretty clear and imminent danger that it could very well happen again," Pence said.
Pence says a number of factors indicate the suspect is probably a local.
Jessica's backpack was found in Superior and her body was found in Arvada.
"You're dealing with a mentally deranged person," Pence said. "The Denver area public needs to be concerned, not panicked.
He says part of being concerned is being aware. If you see something, say something.
Van Zandt says, right now, every bit of information is helpful.
"We have to be on the lookout. We can't lose another precious child like this. The public's job is to give the information to the authorities. The authorities should investigate," Van Zandt said.
He says the investigation includes canvassing big events like Jessica's memorial service.
Hundreds of officers are working day and night to catch Jessica's killer.
"There will be an arrest made in this case," Van Zandt said. "There will eventually be justice," Van Zandt said.
The volume of tips coming into the Westminster Police command center is staggering.
More than 4,000 tips have come in so far, with hundreds of new leads every day.
On Tuesday alone, Westminster police said they received more than 350 tips.
"Law enforcement will be using every tool, every vehicle that they have," Pence said.
That includes examining forensic evidence, acting on tips, and using the latest technology to track potential suspects.
Investigators will do anything and everything possible until they catch the killer.
"It's a tense community. But it's an outraged community. And there will be a lot of pressure on everyone to get this solved quickly," Pence said.
The FBI says the public should look for unusual behavior such as missing work and appointments, leaving town, changes in alcohol or drug use and even changes in appearance.
Officials say the killer could be a co-worker, a friend, or even a family member.
If you suspect anything, no matter how insignificant you think it may be, you're asked to call 303-658-4336.
(KUSA-TV © 2012 Multimedia Holdings Corporation)