Oddly enough it would be right to withhold immediate judgement on who did this.
Clearly Islamists would be the most obvious suspects and given the insurgency in the south in which tourists have occasionally been targeted you couldn’t rule them out.
But.
This is SE Asia, the political events you see are often not quite what you think is going on. The Islamists have never targeted Bangkok before (I think), there is ongoing political turmoil going on in Thailand, turmoil that led to open warfare in the streets of Bangkok a few years ago. There is serious opposition to the government and indeed this intersection is where the protestors often gathered.
So while the jihadis are certainly chief suspects, I wouldn’t rule out other agencies, at least not for the time being.
From the Daily Mail article linked above:-
A TIMELINE OF RECENT BLASTS IN THE THAI CAPITAL: HOW BANGKOK HAS BEEN SUBJECTED TO OTHER EXPLOSIONS
2010 -
April: Five grenade blasts hit Bangkok, targeting hundreds of pro-government supporters in attacks that leave one dead and scores wounded, including foreigners. The grenade blasts come after a failed attempt by authorities to disperse the Red Shirts, sparking clashes that left 25 people dead and more than 800 injured in the worst civil unrest in almost two decades.
July: The government says a bomb that killed one at a bus stop in central Bangkok was designed to create disorder.
September: Bangkok put on high alert after a series of grenade blasts. Thousands of police and soldiers are mobilised for extra security.
October: A blast at an apartment complex kills four, with the government blaming the incident on the anti-government ‘Red Shirt’ movement. The Reds deny any involvement and accuse the authorities of a plot to justify tougher security powers.
November: A grenade is thrown onto a minibus killing one. It was not clear if it was politically motivated.
2011 -
January: Police arrest five men armed with explosives after a tip-off that bomb attacks were planned near the seat of government in Bangkok.
June: Two people are injured in a blast at a political protest by Thailand’s ‘Yellow Shirt’ demonstrators near Government House.
December: A makeshift explosive device is found and defused near the government lottery office with authorities saying the perpetrators wanted to ‘challenge the government’.
2013 -
May: A homemade bomb hidden near rubbish bins in a busy suburban Bangkok shopping area explodes, injuring seven people.
2014 -
January 18: One protester dies after a bomb attack at an opposition march in Bangkok. Authorities and demonstrators blame each other for the blast, which was apparently caused by a grenade-type device thrown from a nearby building.
January 19: Twin blasts by unknown attackers at an anti-government protest in central Bangkok leave 28 injured.
2015 -
February: Two small bombs explode near a popular shopping mall in downtown Bangkok. One man is injured but there are no deaths.
August 17: At least 16 people - among them foreigners - are killed after a blast in Chidlom district at a popular shrine located on a main road through Bangkok’s commercial hub.