SINGAPORE - A 33-year-old man who sent four identical threatening messages to Prime Minister Lee Hsien Loong's Facebook account earlier this year was convicted on a charge of criminal intimidation on Tuesday.

Tan Yeong Hong also pleaded guilty to two counts of hurting two policemen.

The court heard that Tan believed he had been approached 10 years ago by an unnamed Chinese man, and was instructed to pass "data" to Mr Lee.

At about 8pm on June 24 , 2015, he went to Mr Lee's Meet-the-People session to pass him an article that he had typed.

Tan carried a black haversack containing a hammer, but said he had no intention to use it.

As Mr Lee was not present, Tan passed the article to a grassroots leader.

Later that night, Tan used his mobile phone to send the four threatening private messages to the Prime Minister's Facebook account.

The messages, sent at at 8.49pm, read: "Eh, You challenged me to visit your MPS but you are not here. I will find and stage an Attack on you when I have information on your Public Appearances. You know who i am". Tan also included his IC and mobile phone numbers.

Tan claimed he was prompted to do so by "someone with a hidden audio and surveillance device planted in my house".

Subsequently, "the people in the audio and surveillance system" in his house told him to find Mr Lee when he made a public appearance, Tan said.

Tan was asked by the voices he heard to throw a hammer at Mr Lee, "because he refused to take the document from me after he had asked me to prepare it."

Tan then checked Mr Lee's Teck Ghee ward Facebook page to determine his next public appearance, which he wrote down on a piece of paper.

Shortly after 2 pm on June 25, a senior manager from the Prime Minister's Office lodged a police report about the four messages.

The police ascertained Tan's identity later that day, and officers who interviewed his parents were told that he was a violent person who always armed himself with a knife, which he kept inside his bag.

When four officers approached him at the carpark below his block in Hougang Avenue 1 at about 7.55pm the same day, he refused to disclose his identity and turned hostile.

Tan threw a punch at Senior Staff Sergeant Cheong Kok Leun and then elbowed Staff Sergeant Ryan Tan Yik Mong. He was subdued and arrested.

A search of his home uncovered a bag containing a hammer and a chopper and several knives, among other things. There was also a piece of paper in the bedroom listing Mr Lee's potential public appearances.

On Tuesday, Deputy Public Prosecutor Andre Chong urged the court to impose a total sentence of between 18 and 23 months' jail.

While Tan was suffering from Paranoid Schizophrenia at the time of the offence, a report from the Institute of Mental Health found that he was not of unsound mind at the same time. He was also found to be fit to enter a plea in court.

In his mitigation, Tan, who did not have a lawyer and has been remanded since his arrest, said: "I did not know that the charges are so severe."

District Judge Matthew Joseph said that it was "in the interest of justice and fairness" that Tan be assigned a volunteer defence lawyer by the court, given the IMH report and the nature of the charges he was facing.

The case will be heard again on Oct 15.

The offence of criminal intimidation carries a jail term of up to 2 years and a fine. For hurting public servant in the discharge of his duty, Tan could be jailed for seven years and fined and caned.