Sorry about the delay. I’ll make it up by posting four articles that touch same subject – the tragic death of Yuri Gagarin.

Yuri Gagarin, The first cosmonaut dies in plane crash

MOSCOW (PAP). The Central Committee of the CPSU, the Presidium of the Supreme Soviet and the Council of Ministers of the USSR with deep regret inform that on 27 March 1968, following a plane crash during a training flight in an airplane, the first cosmonaut of the world, famous aviator-cosmonaut of the USSR, member of the Soviet Communist Party, deputy of the Supreme Soviet, Hero of the Soviet Union, Colonel Yuri Gagarin has lost his life.

In the same plane crash the commander of the air unit, a member of the CPSU, Hero of the Soviet Union, Colonel Vladimir Sieriegin engineer was also killed.

The Central Committee of the CPSU, the Presidium of the Supreme Soviet and the USSR Council of Ministers express their deep sympathy to the families and relatives of the deceased.

The Central Committee of the CPSU, Presidium of the Supreme Soviet and Council of Ministers decided to form a government comission including member of the Politburo to organize the funeral of Gagarin and Sieregin and being led by secretary of the CPSU Central Committee – Andrej Kirilenko.

Gagarin and Sieriegin will be buried on Red Square in the Kremlin Wall.
 

Source file: link
 

This is probably the first article that was published in polish newspapers informing about the plane crash. Note typical for that time certain way of writing political expressions that sound like gibberish. It’s hard to say when it was published exactly – probably a good number of days after 27th of March. Probably in April. It would also seem that they couldn’t decide how to write ‘Sieregin’.

Yuri Gagarin was born on 9 March 1934. April 12, 1961 was the year the spaceship “Vostok I” made the first spaceflight in the world reaching Earth’s orbit (apogee 327 km, perigee 175 km) and landing on the designated territory of the USSR (around the village Smielovka in Saratov Oblast). Flight lasted 108 minutes at a speed of 28 thousand kilometers per hour. During his first journey to Space, Gagarin flew 40 thousand kilometers.

MOSCOW (PAP). – The Central Committee of the CPSU and the USSR Council of Ministers formed a government commission to clarify the circumstances of the tragic death of the world’s first cosmonaut, Yuri Gagarin and colonel Sieregin who both lost their lives in the crash during flight training.

Source file: link

I’m not sure if this part was below the article or is from a completely different source. It might have been included below main text which sounds like it was translated from official soviet document to make it up to date.

Circumstances of the tragic death

MOSCOW (PAP). A government commission established to clarify the circumstances of the death of Gagarin and W. Sieriegin reported that the plane, which they used crashed near the village Nowosielkovo in Vladimir Oblast.

On 27th March during daylight Gagarin took off from airfield near Moscow for his next flight with Sieriegin (an instructor) in the two-seater trainer jet to train piloting technique. The plane crashed on its way back to the airport after the completion of the training task.

Source file: link

This is the first official confirmation of the crash site mentioned in polish press – most likely dated to early April, few days after the incident.