(CNN) A Texas Ranger who investigated the Botham Jean shooting said Wednesday that the ex-Dallas police officer who killed Jean in his own apartment was reasonable to think he was a burglar.

In fact, Sgt. David Armstrong said, the investigation leads him to believe authorities had no probable cause to arrest Amber Guyger for any crime.

"I don't believe that (the shooting) was reckless or criminally negligent based on the totality of the investigation and the circumstances and facts," Armstrong said.

District Judge Tammy Kemp did not allow Armstrong to deliver the testimony to the jury, saying she would not let him speak to the reasonableness of Guyger's actions on the night of September 6, 2018. Several of Jean's neighbors testified about what they heard on the night of the shooting, and a medical examiner testified about Jean's injuries.

Though prosecutors allege Guyger murdered the 26-year-old accountant, her defense team has said she simply walked into the wrong apartment and fatally shot Jean after mistaking him for a burglar. Jean's apartment was on the floor above Guyger's.

Were Guyger's fears and actions reasonable?

Day three of Guyger's murder trial began with Armstrong's testimony regarding the investigation -- which included details on the many similarities between the third and fourth floors at the South Side Flats complex -- yet when it came to the reasonableness of Guyger's actions, Kemp excused the jury so she could determine whether Armstrong's testimony would be allowed.

Investigators interviewed 297 residents at the apartment complex, Armstrong said, and many of them told authorities they'd parked on the wrong floor, walked to the wrong apartment or even put their keys in the door of the wrong apartment by mistake. Armstrong parked on the wrong floor himself during the investigation, he said.

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The percentage of people who'd experienced such confusion grew when police interviewed residents of the third and fourth floors, where Guyger and Jean lived, he said. For instance, while 32% of residents said they'd parked on the wrong floor, 47% of residents on the third and fourth floors said they had parked on the incorrect level.

Also, the locking mechanism on Jean's door was damaged, Armstrong said, affecting the door's ability to shut properly, which Guyger's defense team said is one of the reasons she thought someone was burglarizing her home.

The circumstances led Armstrong to believe Guyger was reasonable to think she was walking into her own apartment, reasonable to believe there was a burglar inside and reasonable to perceive that Jean posed a threat, he said.

Asked directly by defense attorney Robert Rogers if he believes there was probable cause to arrest Guyger for any crime whatsoever, Armstrong replied, "Based on the totality of the circumstances, based on the complete investigation, no sir."

Ranger: Guyger experienced 'fight or flight'

Tuesday's witness testimony indicated that the prosecution seeks to demonstrate Guyger did not follow department protocol for a burglary call.

Protocol dictates she should've taken cover and called for backup, at least one of her fellow officers testified, but the defense proffered that because she was off-duty and thought she was walking into her own home, she should not be held to that standard.

Armstrong agreed with the defense assertion, he said, describing what he thought Guyger was feeling when she encountered Jean.

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"Physically your heart rate goes very, very high. Your vision becomes narrowed, which is commonly referred to as tunnel vision," the Ranger said. "You begin to think very, very quickly and because your vision is narrowing, you begin to concentrate on what you believe your threat is ... and that's due to blood rushing to the major organs of the body because your body is saying 'I need to do this right now,' which is either fight or flight."

Prosecutor Jason Hermus told Kemp he objected to the testimony because Armstrong wasn't qualified to speak to Guyger's state of mind and worried aloud that the Ranger offering his opinion could confuse jurors.

"What Ranger Armstrong believes is Ranger Armstrong's opinion," he said. "His opinion and belief doesn't help the jury. ... The fact that he believes something based on evidence doesn't mean the jury is going to believe the same thing."

Rogers argued that Armstrong was only opining on the reasonableness of Guyger's actions, which the prosecution put in play by raising the issues of the Dallas Police Department's protocols on burglary calls and all the cues Guyger missed indicating she was on the wrong floor and entering the wrong apartment.

Medical examiner: Bullet traveled in downward motion

Alyssa Kinsey, one of Jean's neighbors, testified she was on FaceTime with her boyfriend on her living room couch when she heard "very loud sort of metallic sound."

Seconds later, she heard commotion from the hallway area that sounded like a man and woman yelling. "It sounded like running or slamming, something like that," she said.

Soon after, she heard what sounded like a woman calling 911. Kinsey heard the woman say, "apartment 1478" and "shot." Jean lived in apartment 1478.

While still on the phone, Kinsey went out on her patio, which is about eight inches from Jean's patio, and saw the lights were on in his apartment.

She heard police arrive and discuss performing CPR.

The Dallas County medical examiner who performed the autopsy on Jean testified the bullet entered above his left nipple and traveled downward through the chest, hit a rib and struck his lung and heart. It moved through the diaphragm, struck the stomach and intestines, stopping in a muscle in the abdominal cavity close to the spine, Dr. Chester Gwin said.

Gwin could not say where either the shooter or where Jean were positioned but agreed that Jean was likely bent over in some capacity or even on his back when he was shot.

Hermus held a long stick against his chest and bent over to demonstrate the direction of the bullet to jurors.

"Unless the shooter is on the roof of this room and shooting down, although that's a possibility, that's probably unlikely. Would you agree with that?" Hermus said.

"I would say that's an unlikely scenario," Gwin said.

Rogers has argued Jean was advancing towards Guyger and she felt she "had no choice" but to shoot him to save her life.

'Was that evil of her to do?'

No one is arguing that Guyger shot Jean, but the prosecution aims to paint her as negligent and claims she was texting a lover during the 911 call and did too little to save Jean after she shot him. Guyger has said she provided first aid to Jean, according to an affidavit.

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The former officer's defense team is countering that she was fatigued after working more than 40 hours in four days and was not paying attention when she parked in the garage, where the floors are not clearly demarcated, he said.

"Was that evil of her to do? Was that evil of her not to count the floors? Was that just a reasonable reaction to 'Oh my gosh I found a good spot?'" Rogers said during opening statements.

The defense could call Guyger to the stand later this week, though the exact timing is not clear.

The prosecution will continue to present its case on Thursday.