Without looking at any other information, two theories about yesterday's Kharkov explosion have a right to exist: either it was done by the Kiev junta or by it's opponents.
Kiev junta of course is a terrorist government. It came to power by provocations and resorted to provocations in order to stay in power. As soon as it was done with one provocation it would begin plotting the next. If the information above is indeed true, then the Kiev junta could kill two birds with one stone: get rid of a key witness and earn some reputation points by "proving" that the "separatists" are indeed "terrorists", just when the public opinion was shifting away from the war after Kiev's devastating loss of 3,500 soldiers in Debaltsevo.
If it was done by the "Kharkov anti-junta underground", then they could set out to eliminate a key participant of the Odessa massacre, and terrorize junta supporters, who are not welcome by the majority Russian-speaking Kharkov. But then they would be resorting to the same tactics as the junta. No doubt, that it is possible that there could be some in the resistance who could turn to such methods on their own, just like the anti-fascist underground in the 1940's. But it would also be a gift to the junta and the Western media supporting it in justifying their narrative and would be contrary to the overall mission of the anti-junta movement to create an all-inclusive truly democratic society without terror and nationalist slogans in Ukraine (or at least their own regions-republics). Such an act is a mass murder and and should result in a highest form of punishment of the perpetrators by the leaders of the resistance, if that's the case, because it goes against everything that the resistance stands for, and this is why it has a signature of the Kiev junta.
At least 700 people have been detained in Kharkov on charges of separatism, and Kharkov was of course the only other city besides Lugansk and Donetsk, were the resistance had seized the regional administration building in April, with a goal to set up a Kharkov Republic. In a way Kharkov saved Lugansk and Donetsk, since it was geographically closer to Kiev and was the only location were the junta could manage to direct it's storm troopers, who stormed the building arrested the activists inside, and surrounded it's perimeter, but would not respond to locals' questions in Russian or Ukrainian.
The fact that administration buildings were seized by the Right Sector and other militants (previously trained for years in Poland and Lithuania) in Western Ukraine and downtown Kiev as part of a coup to overthrow the government of Yanukovich did not seem to upset junta's Western backers.