PRETORIA, South Africa (CNN) -

Oscar Pistorius was in a "loving and caring relationship" with Reeva Steenkamp, the girlfriend he is accused of murdering, the sprinter's agent testified Tuesday.

Pistorius involved his girlfriend in conversations about business and wanted her to travel with him so she could see what his life was like, Peet van Zyl said on the stand at the athlete's murder trial.

He was excited about taking her to a concert by Italian opera singer Andrea Bocelli, the agent said.

The double amputee sprinter is on trial for killing Steenkamp in February last year. He admits killing her but says he mistook her for a burglar and thought he was defending himself.

The prosecution says the two had an argument and he killed her intentionally.

Van Zyl described the sprinter as "hypervigilant" and "always fidgety," saying Pistorius once grabbed his arm when they heard a bang on a street in New York, and liked to sit where he could see the exits when they went to restaurants.

But he denied that the athlete was prone to outbursts of anger.

Van Zyl had lost his temper more often than Pistorius during the years they worked together, he said.

The main Pistorius defense lawyer, Barry Roux, questioned van Zyl Tuesday morning before handing him over to prosecutor Gerrie Nel.

Nel, an aggressive, sometimes sneering interrogator, attacked van Zyl from the outset, pressing the agent to say part of his job was to deal with Pistorius' bad press.

But Nel did not question van Zyl for long before requesting an adjournment for the rest of the day. He said he was not expecting van Zyl as a witness and needed more time to prepare to question him about the athlete's character.

The hearing concluded for the day before lunch and will resume on Wednesday for its 36th day.

Screams like a woman?

Van Zyl took the stand after an acoustics expert, Ivan Lin, was cross-examined about sounds on the night of killing.

Some neighbors have described hearing a woman's screams between shots the night Steenkamp died, which the prosecution suggests was the argument that led to her death.

But the defense has argued that Pistorius sounds "like a woman screaming" when he's anxious, and says it was his screams that ear-witnesses heard.

On the stand for the defense Monday, Lin said "typically" one can differentiate between male and female screams, but not without exception.

Nel pressed him on the point but made little headway on Tuesday.

The prosecutor did get Lin to concede that state witnesses could have heard screaming from the Pistorius house on the night of the killing from their homes up to 177 meters (580 feet) away.

Mentally sound