'My goal is to kill cops today': Chilling words Colorado cop killer posted online before he gunned down 19-year-vet before being shot dead by hero bystander who was then killed by police in tragic mix-up

Authorities have released chilling excerpts of a four-page letter written by a Colorado man before he shot dead a police officer with an AR-15. 

Ronald Troyke, 59, was caught on surveillance camera gunning down officer Gordon Beesley, 51, in the town of Arvada on Monday afternoon. Good Samaritan John Hurley, 40, was shopping nearby and rushed to the scene with his concealed carry pistol.

Hurley shot dead Troyke, potentially saving the lives of other officers and civilians in the process. Hurley then picked up Troyke's AR-15, causing cops who subsequently arrived on the scene believed he was the original gunman. Tragically, they shot him dead in a case of mistaken identity.

The Arvada Police Department has admitted the fatal mix-up and hailed Hurley as 'a hero'. 

They have now also released excerpts of a disturbing letter Troyke penned prior to his murder of Officer Beesley on Monday. It was reportedly uncovered inside Troyke's home. 

'My goal today is to kill Arvada PD officers,' the letter, obtained by Fox31, reads. 

'Hundreds of you pigs should be killed daily,' he added. 'I just hope I don't die without killing any of you pigs'.

Officer Gordon Beesley, 51 (left) was killed by Ronald Troyke in Arvada, Colorado, on Monday afternoolGood Samaritan John Hurley, 40

Officer Gordon Beesley, 51 was killed by Ronald Troyke in Arvada, Colorado, on Monday afternoon. Good Samaritan John Hurley, 40 , also lost his life after reportedly confronting the gunman 

 The letter continued: 'Today I will kill as many Arvada officers as I possibly can'. 

It also featured the sentence: 'This is what you get, you are the people who are expendable'.

Meanwhile, surveillance footage from the incident shows Troyke parking his dark-colored pick-up truck in Arvada on Mondau afternoon, just minutes before he shot and killed Officer Beesley. 

The video clearly shows Troyke exit the vehicle at 1.35 pm dressed in a black shirt and shorts, openly brandishing his AR-15. 

He then runs towards an unsuspecting Officer Beesley before shooting him dead. 

Eyewitness Bill Troyanos told The Denver Channel he was working in a nearby store at the time, and Hurley was inside the premises doing some shopping. 

The pair heard he gunfire, before Hurley - who was armed with his own concealed carry - ran out of the shop towards the scene. 

'He did not hesitate; he didn't stand there and think about it,' Troyanos told the station. 'I just want to make sure his family knows how heroic he was.'

According to Troyanos, Hurley confronted Troyke and fired five or six shots at him, causing the gunman to collapse against a parked car.

A manager at another nearby business told the station that prior to the shooting, he heard Hurley urging bystanders to seek shelter.

'He turned back and looked towards everybody at the restaurant and told us that he the is coming, that he is coming back and that we should get inside,' the manager said.   

Gunman Ronald Troyke on CCTV moments after he had ambushed and killed Officer Beesley

Gunman Ronald Troyke on CCTV moments after he had ambushed and killed Officer Beesley 

Police officers investigate the scene the shooting in  Arvada on Monday, which left Beesley, Hurley and the gunman dead

Police officers investigate the scene the shooting in  Arvada on Monday, which left Beesley, Hurley and the gunman dead

Meanwhile, the district attorney's office has not commented on whether or not charges could be filed against the cop who fired the shot that killed Hurley.

Arvada police did tell The Denver Post that an officer is on administrative leave, which is considered to be standard protocol, but didn't reveal their identity. 

According to his Facebook page, Hurley was a classically trained cook. Until recently, he had been working for a catering company. After the business declared bankruptcy, Hurley took on jobs at a piano-moving company and an arcade, reported Fox 31.

Long-time friend Cody Soules described him in a statement as 'an outspoken activist' who wanted to help people in his community. 

Hurley's former co-worker Cole Crocker told Fox 31 that he was dedicated, passionate and caring. 

'Johnny was the kind of guy that would think of everyone but himself first, always,' he said.  

Sources say a police bullet was responsible for killing Hurley during Monday's shootoutSources say a police bullet was responsible for killing Hurley during Monday's shootout

Sources say a police bullet was responsible for killing Hurley during Monday's shootout

Beesley, 51, 'was targeted because he was wearing an Arvada police uniform and a badge,' police Chief Link Strate said at a news conference on Tuesday.

'Officer Beasley was ambushed by someone who expressed hatred of police officers.' 

Beesley was a school resource officer with a reputation for taking a compassionate approach with students. 

With school out for the summer, Beesley was working on patrol when he was hit by gunfire shortly after a report of a suspicious incident that police also have not described.

Beesley was a 19-year veteran of the Arvada Police Department, working as a patrol officer and as a motorcycle traffic officer before working as a school resource officer. He is survived by wife Karen and their two children. 

According to court records cited by The Denver Post, Troyke was convicted of third-degree assault in 1992 and DWI in 1994. He was evicted from his home the following year, and in 2013 he declared bankruptcy. 

There is no indication that Troyke had had any major run-ins with the law over the past 17 years.   

Police in Arvada, Colorado, were called to reports of gunfire at around 1:30pm on Monday

Police in Arvada, Colorado, were called to reports of gunfire at around 1:30pm on Monday

Spencer Tscherpel, left, and his wife Paige, who live in the neighborhood, embrace as they watch police officers line up for a procession honoring Beesley

Spencer Tscherpel, left, and his wife Paige, who live in the neighborhood, embrace as they watch police officers line up for a procession honoring Beesley