An autistic Adelaide teenager who took a working pipe bomb on a public bus had no insight into how the community would react until he saw his crimes in a news report, a court has heard.

Key points: The boy's lawyer said his client was under the impression the bomb would impress his friends

The boy's lawyer said his client was under the impression the bomb would impress his friends The teen told the court he was "disgusted" with his actions and was seeking forgiveness

The teen told the court he was "disgusted" with his actions and was seeking forgiveness Prosecutors want a penalty that will allow the boy to be released under supervision

The 17-year-old — who cannot be named for legal reasons — today faced a pre-sentencing hearing in the South Australian District Court, where he stood and read a letter of apology.

"I admit that I don't really know how to start — I was never particularly good at articulating how I feel or think," he told Judge Barry Beazley.

"I feel a certain type of disgust in myself. Disgust because I did not take into account free will.

"I had such idealistic goals — I would fix the chasm between my friends, I was going to once again have that feeling of friendship and a bond of trust that I had felt so strongly just four years before."

The court heard the boy became marginalised and friendless in the lead-up to his decision to make the pipe bomb, falsely believing it would strengthen bonds with his friends.

He said he had never thought about the "free will" of his former friends and did not contemplate that they should be free to choose if they wanted to spend time with him.

"How could I not think of personal freedom? The idea of free choice and independence is at the heart of my moral compass," he said.

"And yet I had become a manifestation of the very thing I hated."

The boy pleaded guilty to two counts of taking steps to manufacture an explosive device, one count of possessing an explosive substance and one count of possessing an explosive device in a public place.

TV report made teen realise 'gravity of situation'

The court previously heard the pipe bomb was in "working order".

At the time, police said CCTV footage showed the teen on a bus, which was travelling through Adelaide's south, in possession of the device.

He did not activate the device and no-one was harmed.

"The gravity of my situation came to me not long after my incarceration, I saw the news report on me while I was in my cell and I saw how the greater community viewed my actions," he told the court.

"The sickness in my stomach, the disgust in my actions and the realisation at what I had done.

"I have no excuses for my choices, I cannot justify my actions, I cannot undo the consequences, but what I can do is, and what I hope to do, is seek forgiveness — not just from my family and my friends, but from the greater community.

"I'm truly sorry."

Complaint filed about boy's treatment in youth detention

The boy's lawyer Stephen Ey told the court the his client did not understand "the enormity" of what he was doing because of his autism.

"He is adamant it was never his aim to hurt anyone," Mr Ey said.

He said the boy was "shocked" at his friend's reaction when he showed her the bomb, falsely believing it would instead rekindle their friendship.

The teenager has apologised in court after taking a pipe bomb onto an Adelaide bus in 2019. ( ABC News )

"He envisaged them thinking, 'he's got a bomb, we'll go with him and they'll be all together and everyone would be friends again'," he said.

He said the boy's mother had made a complaint to the Guardian for Children and Young People about the way her son has been treated in youth detention.

Prosecutor Alex Rathbone said she was not seeking further detention of the boy, but rather wanted a penalty that would allow him to be released and be supervised in the community.

"This is very serious offending, that created a situation of potential danger to people known to [him] and to strangers," she said.

"When he is released from custody, the most effective thing to do is structure a sentence that has him under supervision for a significant time so when he's in the community, he continues with his therapeutic treatment."

Judge Beazley will sentence the boy next month.