Inside the house of Omar Mateen, a hateful mass murderer who loved his toddler

FORT PIERCE. Fl - Family photos and drawings of his three-year-old son decorate the apartment of the perpetrator of the deadliest shooting in U.S. history, 29-year-old Afghan-American Omar Mateen.

On a blackboard in the kitchen, a message reminds Mateen and he and his wife have an appointment at their son's school on July 13. Another note bears the Arabic phrase "Al Hamdullillah" (Praise God).

Univision News visited Mateen's unoccupied house on Monday, the morning after it was swept by the FBI for evidence related to the attack on the Orlando gay club, Pulse, where Mateen opened fire with an AR-15 military-style assault rifle, killing at least 49 people early and injuring another 53. The apartment was unlocked and had not been sealed off by yellow crime scene tape.

On the living room table, there was a document listing the objects removed by investigators: 9mm cartridges, an iPad mini, a Samsung phone, a Dell computer, a CD labelled with Mateen's name.

Mateen, who was killed by police in a shootout, lived with his second wife, Noor Zahi Salman, 30, and their three-year-old son on the first floor of an apartment building in a working-class neighborhood in Fort Pierce, about 120 miles south of Orlando. The house has two bedrooms, two bathrooms, a kitchen and living room.

Salman grew up in Rodeo, California, northeast of San Francisco. After the shooting she deleted all her social media profiles and appears to be in hiding, though some media reports say she is cooperating with authorities.

In the house is a Koran and several books books on Islam. On a double bed sits another book: "Being Palestinian Makes Me Smile" signed by the Arab-American author Amer Zahr, a 38-year-old U.S.-born stand-up comedian and Detroit history professor.

Contacted by Univision News, Zahr was shocked to learn his book had been found in Mateen's apartment, and described it as "the last kind of book" that would inspire an act of terrorism.

"It’s about seeing life from a Palestinian perspective with a mixture of comedy, some of it dark, and politics," said Zahr, adding that it is a collection of blogs written between 2009 and 2014. "I talk about the perplexity of the Arab and American identity."

The son of Palestinian refugees, Zahr's mother is Christian and his father Muslim, but he doesn't count himself as particularly religious.

“My family are from Nazareth," he said, referring to the largest Palestinian city in Israel, with a largely Christian population. "Jesus is one of us. That’s what I tell my friends,” he added.

Zahr said Mateen likely purchased the book at a convention for Palestinian emigres where Zahr spoke in Orlando in December 2014. “I guess he was there. I signed the book. But I don’t remember him at all. I probably signed between 100 and 120 copies at the convention," he said.

In the living room, Mateen had weights and an abdominal exerciser. Mateen was a muscular man who like to work out and took muscle-enhancing substances, according to acquaintances.

Mateen’s neighbors were ordered to evacuate the two-story building on Sunday as a preventative measure in case he had booby-trapped his apartment with bombs. By Monday morning, there was no sign of residents having returned after investigators had departed.

Mateen was born in New York but grew up in Florida. He regularly attended the local mosque in Fort Pierce with his parents and three sisters, as well as his son.

He earned an associate degree in criminal justice in 2006 and a year later was hired by one of the world’s largest security companies, GS4.

His first wife, an immigrant from Uzbekistan, divorced him in 2011 after two years of marriage, during which she says he abused her. Mateen was bipolar, she told reporters on Sunday outside her home in Texas.

The FBI began investigating him in 2014 after co-workers alerted authorities about Mateen’s possible links to terrorists. The officers closed two investigations without finding evidence.

Those who knew him describe him as unfriendly, but in photos found in his apartment Mateen appears with his son smiling. The boy's room was stuffed with toys, including Disney and Marvel superhero accessories.

His mosque, the Islamic Center of Fort Pierce, blames the internet for Mateen's radicalization. The imam and dozens of regular attendees say the mosque preaches a moderate Islam that condemns ISIS and does not issue messages of hate against homosexuals.

The second imam, Mefzi Adel, said Mateen always arrived at the center holding his son's hand. "He was a loving father. He always hugged and kissed his child. I'm surprised he did this and did not think of his son," Mefzi said.

A family friend, Bedar Bakht, told Univision that Mateen had changed recently. Bakht lived for five years in Maryland and was reunited with Mateen two months ago at the mosque. When he saw him, he was surprised how distant Mateen seemed.

"As a child he was rebellious, very talkative and curious, always asking questions," Bakht says.

Bakht said that when he saw Mateen's son he was reminded of his own son, now in college. "I said, 'how he has grown!' He laughed and gave me a hug, but he didn't want to talk more."

Additional reporting by David Adams, Rachel Glickhouse and Jessica Weiss