Authorities are offering a $50,000 reward in the murder of a Colorado teenager burned alive inside her family's home in 2017.

At a press conference Monday, Park County Sheriff Tom McGraw revealed that detectives believe 17-year-old Maggie Long was purposely set on fire.

'We believe this was a targeted crime and that there are at least three suspects still at large,' McGraw said.

'Hundreds' of persons of interest have been ruled out over the nearly 14-month investigation by the Park County Sheriff's Office, Colorado Bureau of Investigation, Federal Bureau of Investigation and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

A website where people can submit tips was unveiled on Monday as the hefty reward was offered for anyone who provides information leading to an arrest.

'Somebody knows what happened,' said McGraw. 'Every tip will be addressed.'

The sheriff said it's believed the suspects targeted Long's family home in Bailey but didn't necessarily have prior intention to target the teen.

It's unclear whether the suspects knew Long, but 'it's a possibility', McGraw said.

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Authorities are offering a $50,000 reward in the murder of 17-year-old Maggie Long (above), who was set on fire and burned alive at her home in Bailey, Colorado, in December in 2017. Investigators launched a website seeking tips in Long's murder on Monday

Investigators believe the fire was intended to cover up evidence of a 'physical altercation' between Long and three suspects. Scorch marks can be seen at the home where Long's body was discovered on December 1, 2017

A task force made up of investigators from the Park County Sheriff's Office, Colorado Bureau of Investigation, Federal Bureau of Investigation and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) released the sketches above of two suspects seen in the area after the fire

Long was reported missing after she failed to show up to a concert at her high school on December 1, 2017.

Her body was discovered at the burned home by police that night, but it wasn't until three days later that the county coroner publicly identified Long as the deceased.

The death was ruled a homicide based on the fact that the area surrounding Long's body was so badly damaged by fire.

Last year, investigators said that several guns, a gun safe and jade figurines were stolen from the home before it went up in flames.

They elaborated on Monday, revealing that they believe there was a 'physical altercation' between Long and the suspects, which the suspects tried to cover up with the fire.

'Law enforcement believe the intent of the fire was to conceal actions of these assailants, such as the physical altercation and subsequent robbery,' the tip website says.

Long was reported missing after she failed to show up to a concert at her high school on December 1, 2017. Her body was discovered at the burned home by police that night and she was publicly identified by the county coroner three days later

Last year, investigators said that several guns, a gun safe and jade figurines were stolen from the home before it went up in flames

Authorities said the suspects targeted Long's home (above) but didn't necessarily have prior intention to target the teen

This week authorities released sketches of two alleged suspects in the case along with new photos of vehicles resembling those spotted near Long's family home in Bailey on the day she was killed.

According to the site, one sketch shows a man who was seen in the passenger seat of a Chevrolet Astro-type work van.

A witness also reported seeing vehicles similar to an early-90s Ford Aerostar van and a late-80s Ford F-150 leaving the neighborhood.

McGraw said he believed all three suspects may have significantly altered their appearances, sold their vehicles and moved away from the small Colorado town after the murder.

He said billboards will be posted throughout the state asking for information about the case and directing people to the website, maggielongtaskforce.com.

A description on the site reads: 'This website was created to allow the Maggie Long Task Force to engage with the community and provide a venue for community members to share any information they may have directly with the task force.

'Oftentimes, members of the community have information of value but do not come forward because of concerns that it may not be important or may be information law enforcement already has.

'Please provide any information you have or other details you are aware of, even if you have previously provided the information.'

Update On Unsolved Murder Of Maggie Long Investigators with Park County are providing an update on the unsolved murder of Maggie Long. https://cbsloc.al/2GbteJd Posted by CBS Denver on Monday, 28 January 2019

Park County Sheriff Tom McGraw (above) led a press conference about the case on Monday