One year after the murder of 13-year-old Marrisa Shen shocked the Lower Mainland, police are still struggling to identify a suspect.

The Integrated Homicide Investigation Team marked the grim anniversary of Shen's slaying by providing an update on the case Wednesday in Burnaby's Central Park, where her body was discovered.

"So far, investigators have followed up on over 200 tips from the general public, reviewed over 1,000 hours of video and conducted over 600 interviews," Cpl. Frank Jang said.

But no one has been arrested and no charges have been laid. And despite having identified a number of persons of interest, investigators are not ready to call anyone a suspect in the murder.

Jang assured the public that police haven't given up, and are continuing to tirelessly pursue justice for Shen's loved ones.

"We don't just sit on our thumbs and do nothing. Our investigators have been working on this daily," he said.

"We want to provide those answers to the family, for one, and also to the community."

Police have not narrowed the timeline surrounding Shen's murder; there is still a roughly 5.5-hour gap between when she was last seen, and when her body was discovered.

Surveillance cameras recorded Shen leaving her family's home near the park around 6 p.m., then entering a nearby Tim Hortons on McKay Avenue and Central Boulevard.

The young teenager, who was weeks away from starting high school, can be seen politely holding the door for a stranger as she enters.

She left the fast food chain about 90 minutes later, alone, and wasn't seen again until her body was found in the southeast side of Central Park.

IHIT did release one new picture of Shen Wednesday, but had little new information to share about the circumstances of the teenager's seemingly random slaying. Investigators still have not commented on her cause of death.

"There's a number of reasons why we can't share that information with the public, and that really has to do with the prosecutorial end of things. So there is information we can't share at the moments, but we're hoping one day soon that we will," Jang said.

Shen's cause of death hasn't been shared with her family, either. The deceased's brother, Peter Shen, told CTV News they feel frustrated by the lack of progress in the investigation, and the lack of information they've received from investigators.

"My mom is still quite traumatized by the whole ordeal, and refuses to meet people anymore," he wrote in an email. "My dad isn't faring any better."

The police officers investigating the case understand the family's frustration, Jang said, and they're doing everything they can.

"We wanted answers a year ago," Jang said. "To (Shen's brother) I would say: Don't give up hope. Please believe in us. We're working hard to solve your sister's murder."

Criminologist Rob Gordon says it's not unusual for officers to withhold information as they wait for more leads. He likened investigations into serious crimes to a jigsaw puzzle, saying those working the case need to sort pieces into a picture and make sure there are no bits left over at the end.

"They've got a collection of straws right now and they're unable to build a house from them," he said.

It's also not unusual for something or someone to suddenly turn up, he said, either as a result of a tip or an offender's arrest for another crime.

"Forensics is the strong stuff, but it's not foolproof. But forensics are only useful if you've got a suspect that you can link," Gordon said.

In an official statement released through police, the family issued a public plea to anyone with information that might help catch Shen's killer to come forward.

They revealed that Shen was planning to travel to China to see friends before her life was cut tragically short.

"Those plans never came to pass as Marrisa was taken from us," they said.

"It is difficult to express in words the pain of losing her in this terrible way. We were supposed to see her grow up, but instead we have been deprived of the joy of having her in our lives."

Earlier this year, investigators released a criminal profile outlining behaviours they believe the murderer may have exhibited after Shen's death.

It's possible the killer withdrew from social activities, missed work or scheduled appointments, attempted suicide or displayed suicidal gestures, and showed a keen interest in the media coverage of Shen's murder, according to the profile.

The person also may have increased or decreased their alcohol or drug use. If the killer lived near Central Park, profilers believe the individual might have uncharacteristically avoided the area after Shen was murdered.

Anyone with information on the case is asked to call IHIT's tip line at 1-877-551-4448, or Crime Stoppers at 1-800-222-8477.

Coun. Pietro Calendino said the city has taken measures over the last year to ensure the thousands of people that use the park feel safe while walking its trails.

Bylaw enforcement officers patrol the park on bikes and staff members groom the trails frequently.

Surveillance cameras will be installed in some areas as a result of a report that followed Shen's death, and call boxes will be set up starting next month so that those who feel threatened or unsafe can call the RCMP directly.

Addressing another assault which occurred a few days ago but is not believed to be linked to the case, he said he doesn't believe there is a growing trend of violence in the area.

"The park has been in operation for 50-60 years, and two incidents does not make the park unsafe," the city councillor said.

However, he said the best safety measure is park-goers' behaviour: They should avoid being on dark trails areas alone, and let someone know where they're going and when.

With files from CTV Vancouver's David Molko