Openssl and OCSP

I'm trying to check the revocation of certificates in a script but I'm getting the following error:

unable to load certificate
140735258465104:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:703:Expecting: TRUSTED CERTIFICATE

Here are the steps (using www.google.com as an example).

1. fetch the certificate

   $ echo 'Q' | openssl s_client -connect www.google.com:443 > google.crt
   

2. extract the URI of the issuer

   $ openssl x509 -in google.crt -text -noout | grep 'CA Issuers' | \
       sed -e "s/^.*CA Issuers - URI://
   

   this gives http://pki.google.com/GIAG2.crt

3. fetch the issuer certificate

   $ curl --silent http://pki.google.com/GIAG2.crt > issuer.crt
   

4. extract the OCSP URI

   $ openssl x509 -in google.crt -ocsp_uri -noout
   

   this gives http://clients1.google.com/ocsp

And now the final step:

$ openssl ocsp -no_nonce -issuer issuer.crt -cert google.crt \
      -url http://clients1.google.com/ocsp
unable to load certificate
140735258465104:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:703:Expecting: TRUSTED CERTIFICATE

What am I doing wrong?

EDIT

I just saw that http://pki.google.com/GIAG2.crt is in DER format. Converting it to PEM with

$ openssl x509 -inform DER -outform PEM -in issuer.der -out issuer.pem

brings me one step further, but

$ openssl ocsp -no_nonce -issuer issuer.pem -cert google.crt \
      -url http://clients1.google.com/ocsp
Error querying OCSP responder
140735258465104:error:27076072:OCSP routines:PARSE_HTTP_LINE1:server response error:ocsp_ht.c:255:Code=404,Reason=Not Found

The error kind of makes sense since http://clients1.google.com/ocsp delivers a 404 but the URL is the one stored in the original certificate …

The next question will also be how to automatically detect the format of the issuer certificate but I could use file and see if the file is binary or ASCII.