Police have launched an internet investigation after dozens of angry, desperate messages from a man who killed himself and his nine-month-old son in an apparent murder-suicide appeared on Facebook hours after he was dead.

The messages on the social network site included a lengthy suicide note and a memorial collage.

The bodies of 25-year-old Stephen Garcia and his son Wyatt were found early on Sunday on an isolated dirt trail in California's San Bernardino Mountains.

The discovery came after authorities learned that Garcia had taken the boy during a court-ordered visit and threatened to kill him and commit suicide.

Authorities are looking into whether a third person actually posted the suicide note and collage to Garcia's Facebook account after Garcia prepared the items before his death.

The suicide note included a request for the finder to publish it in its entirety. It also provided instructions for dividing Garcia's belongings and explained that he did not want to live without his ex-girlfriend or share custody of his son.

Facebook postings appear on the website in real time and cannot be time-released, company spokeswoman Brandee Barker said.

Facebook referred other questions about the case to authorities, except to say that when Facebook discovers suicidal content on a US member's page, it alerts the National Suicide Prevention Lifeline.

Court records show the baby's mother filed a request for a restraining order in San Bernardino County Court in December, but it was denied on January 12 because Garcia was not considered a "threat to petitioner or the minor child".

An attorney who represented Garcia during the family court cases did not return a call.

Garcia's Facebook page offered a chilling window into his state of mind as he frantically tried to win back his estranged girlfriend and full custody of his son.

In the days before his death, Garcia posted a flurry of desperate messages to his ex-girlfriend, along with pictures of him and Wyatt and video clips of the baby at a younger age.

"Are we really going to do this? I want my (expletive) family back, come back before it's too late. Please? Anything?" Garcia wrote before posting a photo gallery of himself with his son.

Garcia also included links to a website that contained dozens of archived text messages, voluminous diary entries in which he rants against his ex-girlfriend for leaving him and letters asking her if she loves her new boyfriend and if she is planning to have a child with him.

"I'm sorry it took me loosing (sic) you to realise what a great family we had and now our son will have to pay for the mistakes we made FOR THE REST OF HIS LIFE," he wrote.

The suicide note was posted to Facebook eight hours after the bodies were discovered, and the memorial collage was added early on Monday.

The memorial features a photo of Garcia and his son sleeping peacefully on a Mickey Mouse pillow, with the dates of their births and joint death overlaid in white cursive script.

A message at the bottom reads, in part: "There! Now we're sleeping with you ... Find it in your heart to forgive me. It's my job to protect him. I know God will welcome our son with open arms."

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