[12][13] In April 1918, as the bitter Finnish Civil War drew to a conclusion, leading SDP members who had not participated in the revolution, including Lonkainen, published a declaration condemning the revolutionaries.

[14][15] This did not protect Lonkainen from the retribution meted out against SDP members by the victorious Whites following the end of the civil war.

[16][17] On 14 May 1918 White prosecutor Immi Savonius announded that 56 SDP MPs, including Lonkainen, would be charged with treason and ordered their arrest.

[18][19] Lonkainen and five other SDP MPs submitted a notice to the White parliamentary authorities stating that they had not taken part in the rebellion.

[23] Lonkainen denied ever attending a session of the Central Workers' Council and claimed that he had never agitated for rebellion and that he had opposed Me vaadimme internally.

[26][27][28] Lonkainen had been ill for some time and was transferred from Sörnäinen Prison to Helsinki Surgical Hospital where he died on 14 November 1918.