Another "known wolf" terrorist, this time in Melbourne, Australia, as a man well known to police as a violent extremist, took a prostitute hostage after killing her bodyguard.  The man, Yacqub Khayre, held off police for two hours before coming out of an apartment building firing a shotgun.  He was immediately gunned down by police after slightly wounding two officers.

Khayre had been acquitted in 2010 of planning a suicide attack on an Australian military base.  He was later sent to prison on an assault charge and was paroled last December 8.  The GPS monitoring device he was supposed to wear was disabled – a fact the police did not realize until the hostage standoff began.

ABC News:

Khayre, a Somali refugee, has an extensive and violent criminal record. He was sentenced in 2012 to 5 ? years in prison on convictions including aggravated burglary after beating a woman in her home.

He was initially denied parole after serving a minimum three years but was released on Dec. 8, Deputy Police Commissioner Shane Patton said.

Prime Minister Malcolm Turnbull said he would speak with state leaders Friday about changing state laws so that dangerous criminals are not released from prison early on parole.

"There have been too many cases of people on parole committing violent offenses of this kind," Turnbull told reporters.

Police said Khayre booked an appointment on Monday with an escort in an apartment building in Brighton and arrived carrying a sawed-off shotgun, sparking a 2-hour siege.

Police were called after neighbors heard the shotgun discharge as Khayre killed a Chinese-born Australian man employed by the escort agency in the lobby.

Khayre then called police to say he had a hostage in an apartment and made threats to her if police intervened. They tried to negotiate with him before Khayre walked out of the building firing the shotgun.

One police officer was shot in the neck and ear and two officers suffered wounds to their hands, but none of the wounds was life-threatening, Ashton said.

The woman, a 36-year-old Columbian [sic: ABC must mean 'Colombian' –ed.] national, was bound during her ordeal and had been "very significantly traumatized," Patton said. But she had not been physically harmed.

Khayre spoke about al-Qaida in phone calls to police and to Seven Network television, and Ashton said the gunman may have plotted to lure police into an ambush. But it was too early to know if the gunman set out to target police or "seized the opportunity he thought was presented to him," Ashton said.

Ashton said there was nothing to link the violence with a van and knife attacks in London in which three assailants killed seven people.

Police did not regard the Islamic State group's claim of responsibility for the Melbourne violence as evidence that it was planned.

Just who is it that authorities in Western countries are watching if not known violent extremists?  Why do the people they place a low priority on as far as keeping track of their whereabouts and what they might be up to end up killing innocent people?

Why is it a "surprise" when it happens?

The exact same situation existed in Great Britain.  At least one of the London terrorists was well known to authorities for violent tendencies and extremist views. It seems that every "known wolf" terrorist – including the Tsarnaev brothers in the U.S., whom the FBI were well aware of – is somehow able to evade close scrutiny until he ends up on the evening news having murdered innocents.

This is not an argument to watch everybody.  But clearly, the monitoring system currently in place is horribly deficient, and before we can get a handle on these isolated terror attacks, the system is going to have to change.