Ostrava - Police charged Friday four people with the arson attack in Vítkov, which severely injured a Roma family in April this year.
"It is a historic moment in the fight against extremism," police spokesperson Dalimil Sypták told journalists Friday morning.
Sypták added no more details can be revealed due to the ongoing investigation.
On Thursday police in north Moravia arrested 12 people - nine men and three women in connection with the brutal arson attack.
On April 18 a group of unknown arsonists attacked a house in which nine people were sleeping. Three of the family members were severely injured.
The most badly affected was a two-year old baby called Natálka who has suffered from burn injuries covering 80 percent of her body. Natálka has been kept in an induced sleep until this week. The state of her health has slightly improved but still remains serious.
There is not enough evidence for the racial motive of the crime but there are witnesses who heard "Gypsies, your house will burn down!" that night.
