In connection with a police operation in Uppsala earlier on Friday afternoon, three people were picked up from an apartment.
Two of them are suspected of involvement in the act in Vasaparken in Västerås two evenings earlier.
There, a man in his 20s was severely stabbed.
The person suspected of the more serious crime, attempted murder, has previously been arrested in his absence.
But this does not automatically mean that the request is executed immediately when the person is arrested, says prosecutor Stephan Uttersköld.
Hear him in the clip above.