Here, the 22-year-old detonates a homemade bomb outside a villa in Frölunda

"First tape the cobras together and put the stub against the stub so you can light both at the same time. Then tape them to the gas bottle and light." These are the instructions the 22-year-old receives via the encrypted chat app Signal.

But the man lacks gas. Instead, he tapes firecrackers (also called bangers) to a half-liter Coca-Cola bottle, according to his own account, to limit the damage.

- Anyone who stores, transports, places and ignites products like this exposes himself and others to a very big risk, says Johan Gidholm, head of unit at the Total Defense Research Institute (FOI).

Filming the explosion myself

In June this year, the man goes to a villa in Västra Frölunda where he lights the stove and films the explosion himself with a mobile phone. At the same time, he is caught on video by the house's surveillance cameras.

- Once it is lit, you have a number of seconds before it explodes, says Johan Gidholm, head of unit at the Total Defense Research Institute (FOI).

When the 22-year-old runs away, he drops his mobile phone in a hedge. He returns to the crime scene and asks neighbors to borrow a phone. The neighbors then hook him and tie him up with cable ties while waiting for the police.

Pirated copies especially risky

When Johan Gidholm looks at the clips from the police preliminary investigation, he assesses that the firecrackers in the home-made bomb may have been pirated copies. Should that be the case, you don't know what product you have in front of you or what risks are connected to it.

- If you're unlucky, one like this can explode without you lighting it, and carrying it in your pocket can cause very serious bodily harm, he says.

Motive unclear

The man was recently sentenced by the Gothenburg district court to seven years in prison for, among other things, gross destruction of public property and gross illegal threats.

The person behind the Signal account with the instructions has not yet been identified. Nor has the motive been clarified.

- I will not go into the motive, because there we continue to work in other parts of the investigation, says police chief Emil Hagström.