A Twitter posting by an Arizona man who was arrested on suspicion of killing his roommate during a struggle could elevate the severity of charges he could face.

Two days before the fatal shooting, 21-year-old Zachary Dale Penton posted a comment saying he needed to move out of the metropolitan Phoenix home where he was living before he killed his roommates. The comment creates an opening for prosecutors to argue that Sunday's killing of Daniel Garofalo was premeditated, meaning they could charge Penton with first-degree murder and seek the death penalty.

"They will say this kid thought about killing his roommate two days before," Dwane Cates, a criminal defense lawyer in Phoenix who isn't involved in the case.

Penton's attorney says his client's social media posts weren't intended to be taken literally and believes the evidence will show he was acting in self-defense.

Penton, a convenience store manager who had lived in the suburban Gilbert home for two months, told investigators that a physical struggle broke out Sunday when the 41-year-old Garofalo, who owned and lived in the house, came into his bedroom to say Penton had to move out, according to court records. Penton claimed Garofalo had tackled him and took away his phone.

Penton told police that he reached under his pillow for his loaded semi-automatic handgun and fired after Garofalo frightened him by speaking irrationally. He then called 911 to report the shooting.

Police Lt. Hugh White said there were no eyewitnesses to the shooting, so investigators were analyzing physical evidence to determine whether Penton's account is credible. Police also were interviewing two other people who lived at the house.

Over the last three months, a Twitter account in Penton's name had several posts that mentioned guns. The posts included comments on the ease of buying a gun and asked friends whether anyone wanted to go shooting on a particular day. Another post -- perhaps made in jest -- said Penton was forced at gunpoint to download a fast-food restaurant's app.

Penton, who was booked in jail on suspicion of second-degree murder, hasn't yet been formally charged in Garofalo's death.

The Maricopa County Attorney's Office, which will prosecute Penton, declined to comment on whether it will pursue first-degree murder charges.

Joshua Davidson, Penton's attorney, said the shooting wasn't calculated or planned and believes the evidence will show Penton was trying to defend himself in a tough situation. "There are things we all say figuratively every day that, if taken literally, would have a completely different connotation," Davidson said of his client's social media postings.

Penton, who is being held in jail on a $750,000 bond, declined an interview request from The Associated Press.

Cates said the case underscores the need for people to be careful about what they say on social media, where it's hard to convey sarcasm and irony.

"Nobody knows if you are joking," Cates said.