President Yoon Suk Yeol speaks during the 10th hearing of his impeachment trial at the Constitutional Court in Seoul, in this photo provided by the Constitutional Court, Feb. 20. Yonhap

Police said Friday they have booked impeached President Yoon Suk Yeol on suspicion of obstructing the execution of a warrant to detain him last month.

Yoon is suspected of instructing the Presidential Security Service (PSS) to block investigators' attempt to detain him over his short-lived imposition of martial law.

Police reportedly secured text messages Yoon exchanged with PSS deputy chief Kim Seong-hoon via the U.S.-based messenger app Signal on Jan. 3, when investigators attempted and ultimately failed to apprehend him at his residence.

Yoon also gave instructions to block a second attempt to detain him in messages he exchanged with Kim on Jan. 7, according to sources.

Investigators succeeded at their second attempt on Jan. 15, however, and Yoon has since been held at a detention center.

He has been attending a Constitutional Court trial on the validity of his impeachment and a separate criminal trial on insurrection charges related to his declaration of martial law in December.

As a sitting president, Yoon is immune from prosecution except in the case of insurrection, which carries a maximum penalty of life in prison or death. (Yonhap)