After making out with him in the backseat of his rental car around 3 a.m., Katherine Gonzalves broke the news to Rep. Carlos Henriquez that she couldn't go home with him, the 25-year-old recalled on the witness stand at Henriquez's criminal trial Monday.

"His demeanor just changed," Gonzalves testified. She said, "He said, 'I drove all the way out here, into Arlington.' "

Under questioning by prosecutor Clarence Brown, Gonzalves testified that Henriquez "got physical" and back-handed her across the face while the two were in the backseat of the car up the street from her mother's home in Arlington.

"I panicked, started to cry," Gonzalves said, as she told the court the lawmaker punched her three times in the chest and "choked" her before driving away with her in the backseat, unable to open the door.

Gonzalves was at first reluctant to show how Henriquez had allegedly touched her, before assenting and placing two hands around her own neck, as a news photographer's shutter clicked.

Gonzalves paused before answering questions, looking up before giving a reply, and she turned emotional when recounting how she tried to speak to Henriquez some months after the July 8, 2012 incident.

"I just never expected to be here," Gonzalves said, wiping away tears on the witness stand. She said she "felt bad" about "how ugly everything had gotten" and after some drinks with her roommate called Henriquez and arranged a meeting at his house. When Gonzalves's roommate dropped her at the Democrat's home in Dorchester, Gonzalves said two men were out front and told her to leave. Gonzalves said she called Henriquez right afterwards. She said, "I was upset. I felt like I got set up."

Henriquez's defense attorney, Stephanie Soriano-Mills, has based her case on discrediting Gonzalves, highlighting discrepancies between what she told various detectives from the Boston and Arlington police departments.

Gonzalves said she had met Henriquez at a late February community event in Lowell where she had been assigned to interview an attendee. Gonzalves was close to graduating from Middlesex Community College and had taken a class at UMass Lowell as well, she said.

Gonzalves chose to interview Henriquez and said he was "initially like a mentor" before the relationship turned "romantic." In the lead-up to the July 8 rendezvous, the two met about 10 to 12 times. She said, "It was random."

Cross-examination began shortly before the 1 p.m. lunch break, and Soriano-Mills began by questioning Gonzalves about a series of emails she said Gonzalves had sent on March 2, 2012, where Gonzalves said she had seen Henriquez looking at her, said she can "read men," and wrote, "Wait and see what I'm going to be wearing under my coat."

"They were actually flirty," Soriano-Mills said, referring to those initial emails.

"That's what it sounds like," said Gonzalves, who said the email exchange occurred after she had interviewed Henriquez for her paper.

On July 7, 2012, Gonzalves celebrated her younger sister's 21st birthday, going canoeing on a lake where she said she had a drink, consuming a total of three alcoholic beverages over the course of the day. The party returned to her mother's house where Gonzalves said she did not have any more drinks and spent the evening "hanging out" with her sister and a few friends and dancing.

Starting around 8 p.m., Gonzalves and Henriquez exchanged text messages, and as midnight rolled around she made plans to go over to his house, she said. Gonzalves said everyone was asleep in her mother's house, a duplex in Arlington, but as she was leaving her mother confronted her.

"My mother heard me as I was leaving and she got upset because he drove out there to pick me up and she didn't want me to go. It was late," Gonzalves said. She said, "I told her that I would be right back and I was going to tell him to go home."

Gonzalves said she at first got into the passenger seat and spoke to Henriquez before the two entered the back seat and spoke some more and kissed. She said she told Henriquez she could not accompany him, which is when he became angry and hit her.

After the alleged attack began, Gonzalves said, she told Henriquez that she was recording him with her Android cell phone "to scare him" with the hopes he would stop. She said there was a struggle and Henriquez took the phone. At some point, she said, Henriquez threw the phone back at her.

After the struggle over the phone, Gonzalves testified that Henriquez crawled into the driver's seat and took off. She said she was unable to open the backseat door in Arlington and then was able to, when she jumped out of the car near Northeastern University in Boston.

When she left the car, the phone was dead. She said after charging it at home, she realized the SIM card was missing. Later in the morning of July 8, 2012, she spoke with two Boston police detectives, and after that she purchased a new SIM card, Gonzalves said.

In previous testimony with Arlington, Boston and Northeastern University police on the stand, Soriano-Mills has sought to highlight diverging accounts of the timing of the incident, the exchange over the cell phone, her reasons for recording Henriquez and the extent of their relationship.

Earlier Monday, Soriano-Mills asked an Arlington detective whether he thought the discovery of an empty condom wrapper in Henriquez's Zipcar could indicate the encounter was "very different from getting in the back seat to kiss for a little while."

Testimony in the case could finish as early as the end of the day Monday, Soriano-Mills told Judge Michele Hogan. "We'll conference at the end of the day," Hogan said.

Soriano-Mills expected the reminder of her cross-examination of Gonzalves would last approximately an hour and said she had two more witnesses, a police captain and Arlington Police Inspector Gina Bassett. She said she could be done by 4:30 p.m., Monday.